The long-term goal of this project is to elucidate the detailed mechanism of action on a molecular level of enzymes of the blood coagulation and fibrinolytic pathways, especially by use of low molecular weight substrates and inhibitors. At present this research focuses on human thrombin, plasmin, factor Xa, and urokinase. We shall study the specificity of these enzymes using peptide and other synthetic substrates and irreversible and reversible inhibitors. Bovine trypsin and chymotrypsin are also under study as model enzymes, primarily for the development of new types of inhibitors. Methods for the large-scale isolation of human factor X from Cohn fraction III have been developed, and its conversion to and storage as factor Xa will also be investigated.